Normally, when sending email from my domain email address, the recipient’s reply will be delivered to my sender email address.
What I would like to configure is add a Gmail address in Reply-to field so that whenever the recipient replies, I will receive email in my domain sender address as well as Gmail.
There are two ways you can do it, Jarland already mentioned the first way is on each mail client that sends it, the 2nd option is to configure the mail server to modify the email header and add
Reply-To.
I’ve not done it before but I know Postfix is able to modify the mail headers using header_checks that option is only possible if you self host since no provider is going to modify there mail server configs to add that.